Laser cutting of stents has been disclosed in a number of patents including U.S. Pat. Nos. 5,514,154, 5,759,192, 6,131,266 and 6,197,048 and is the preferred technology for stent manufacture in the medical device industry. The conventional approach is to move a hollow tube of metal such as stainless steel under a stationary laser beam. Although the laser is capable of a very rapid cutting speed, the cutting speed of this approach is limited by the speed of the motion drives and in particular the speed of the rotational motor drive.
A typical laser arrangement is shown in FIG. 1. Laser 102 produces a beam 106 which is conditioned as necessary via optical unit 104 and focused into a spot beam which is impinged against hollow tube 108. Hollow tube 108 may be rotated via rotational motor drive 110 and linearly translated via linear motion drive 112.
The conventional laser for cutting is a pulsed Nd:YAG laser which has a pulse duration in the range of approximately 0.1 to 20 milliseconds. This is a long pulse time for cutting and characteristically produces a relatively large melt zone and heat affected zone (HAZ) on the metal. The conventional laser cutting process typically results in the formation of melt dross on the inside edge of the cut tube. This dross must be cleaned off in subsequent processes.
Non-uniformities in the material such as differences in wall thickness create different heat rises in the material and lead to variations in cut quality. Laser parameters have to be re-tuned for optimum cutting for tubes with slightly different wall thicknesses adding to the downtime of the process and reducing the yield.
As the industry moves toward the use of stents having slightly different strut thickness at different positions within the stent, there remains a need for novel methods of rapidly cutting stents from tubes. There also remains a need for developing novel methods of cutting stents from tubes with smaller melt regions and smaller heat affected zone regions than is presently available.
All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well for the purposes of complying with 37 C.F.R. 1.72.
In one embodiment, the instant invention is directed to a method of manufacturing a stent. The method involves cutting a desired pattern in a tube and comprises the steps of providing a tube having a longitudinal axis therethrough, providing a stationary source of laser radiation, generating a beam of laser radiation using the source of laser radiation, and cutting a desired pattern into the tube by scanning the beam over a desired region of the tube.
In some embodiments the laser is scanned or directed over the cutting path multiple times until it cuts through the wall of the metal completely. The laser parameters are set such that on each pass each sequential laser pulse overlaps by a certain amount on the material surface and a small amount of material thereby is removed creating a channel in the material in the desired pattern. Each subsequent pass of the laser creates a deeper channel until finally the last pass of the laser breaks through the bottom surface of the material. This approach has the advantage of minimizing the amount of energy being absorbed into the work piece at one location. This is because after the laser has passed a particular location the heat created in the material dissipates, and also the vaporized material dissipates before the laser returns for its next pass. Because the material vapor dissipates before the next pass of the laser there are no plasma absorption effects as seen in normal multiple cutting (such as when metal vapor is present in the channel or hole part of the laser energy is absorbed creating a hot plasma that in turn causes a larger heat affected zone and recast layer). The multiple scan approach leads to reduced heat affected zone (HAZ), recast material, and slag. Finer details can therefore be cut into the stent shape. This approach is suited to the galvanometer scanning method because of the high speed of scanning.
During the cutting step, the beam may also be deflected about a first axis and about a second axis where the first and second axes are orthogonal to one another and orthogonal to the longitudinal axis of the tube. The beam may be deflected using a single mirror which may be pivoted about the first and second axes. Typically, during the cutting step, the beam is scanned in a circumferential direction by pivoting a first scanning mirror in the path of the beam about a first axis and by pivoting a second mirror in the path of the beam about a second axis, the first and second axes orthogonal to one another and orthogonal to the longitudinal axis of the tube, the first and second mirrors redirecting the beam.
Desirably, the tube is translated in a longitudinal direction relative to the beam during the cutting step.
Desirably, a pulsed laser beam may be used, with the laser pulses having a duration of 100 ns or less. Even more desirably, laser pulses having a duration of 100 ps or less may be used.
Where a pulsed laser is used, the laser beam desirably, may be characterized by a repetition rate of 25 kHz or greater. Desirably, the laser beam is characterized by a pulse power of 108 W/cm2 or greater.
Typically, the laser beam will have a wavelength of 600 nm or less and, desirably, 250 nm or less.
Optionally, the method may further comprise the step of polishing the stent after the cutting step.
In another embodiment, the instant invention is directed to a method of providing one or more openings in a tube for use in manufacturing a medical device. The method involves cutting a desired pattern in a tube and comprises the steps of providing a tube having a longitudinal axis therethrough, providing a stationary source of laser radiation, generating a beam of laser radiation using the source of laser radiation, and cutting a desired pattern into the tube by scanning the beam over a desired region of the tube. The medical device desirably is a stent, vena cava filter or catheter. In the case of a catheter, the pattern is desirably cut into a catheter tube, catheter sheath or catheter bumper.
Additional details and/or embodiments of the invention are discussed below.